1. Field of the Invention
The present invention relates to an apparatus and method for solving blur problems on the surfaces of a light source and an optical window in a photo-induced process, and more particularly, to an apparatus and method for preventing a material produced by decomposition of a reaction gas at the time of deposition of a material by using a photo-induced process, that is, a photochemical vapor deposition (photo-CVD) or a material produced by photo-induced oxidation of a sample, etching, ashing, or the like from being attached to the surface of the light source or the optical window, in a reaction chamber of the photo-induced process apparatus.
2. Description of the Related Art
There is deposition of a material on a substrate, oxidation of a sample, etching, ashing, annealing, surface modification and cleaning, as a photo-induced process. A photo-CVD will be described below as a representative example.
FIGS. 1 and 2 show a conventional photo-CVD apparatus, respectively.
The FIG. 1 technology is disclosed in U.S. Pat. No. 4,654,226. Based on the FIG. 1 technology, a conventional technology preventing a blur phenomenon on an optical window will be described. Referring to FIG. 1, light beams B emitted from a plurality of light sources 100 provided in the atmosphere at the outside of a reaction chamber S pass through an optical window 110 and then are irradiated into the reaction chamber S. Here, if a reaction gas is made to flow into the reaction chamber S in the direction of an arrow mark (←), the reaction gas is decomposed by the irradiated light and thus a thin film is formed on the substrate 120 by using a chemical vapor reaction by a photo-induced process. Meanwhile, a flexible curtain 130 is installed between a substrate 120 and the optical window 110. The flexible curtain 130 is continuously fed at a constant speed at the state where the flexible curtain 130 has been wound up around a lefthand roller in a roll form, and wound around a righthand roller. Here, since the flexible curtain 130 closely contacts the uppermost edge portion of the wall surface in a reaction room which is vertically placed, the reaction gas in the reaction chamber S is not made to reach the optical window 110. However, a sealing between the uppermost edge portion of the vertical wall surface in the reaction room and the flexible curtain 130 is not perfect, the reaction gas leaks from a gap therebetween to cause the optical window 110 to be blurred. Thus, in the FIG. 1 apparatus, a cleaning gas for an optical window purge is made to flow between the flexible curtain 130 and the optical window 110 in the direction of an arrow mark (→), to thereby prevent a blurring phenomenon of the optical window 110.
FIG. 2 is a conceptual view for explaining a process for replacing an optical window blurred in another conventional photo-CVD apparatus, which is disclosed in U.S. Pat. No. 5,810,930. Further, a method for replacing a blurred optical window with a cleaned optical window without breaking a vacuum by using an optical window replacement apparatus, and a method for forming a thin film on a large-area substrate by using a photo-CVD apparatus equipped with an optical window replacement apparatus are also described in the U.S. Pat. No. 5,810,930. The operation of the optical window replacement apparatus will be described below referring to FIG. 2.
When a photo-CVD process is completed at the state where the optical window 200 closely contacts the edge of an upper optical hole in the reaction chamber 210 by a mechanical compression force, an optical window which is blurred by attachment of a reaction product and a reaction gas is transferred to an optical window replacement chamber 220 by means of a mechanical driving apparatus. Then, a gate valve 230 is closed and a nitrogen gas or an inert gas (N) inserted through a first inlet 222, to make the internal pressure become the state of the atmosphere. Then, a cover 240 is opened to replace the blurred optical window with a cleaned optical window 250 and then is closed. Then, the internal gas is discharged through an outlet 224 so that the optical window replacement chamber 220 becomes a high vacuum state, and then the gate valve 230 is re-opened to then transfer the cleaned optical window 250 to an optical window fixing chamber 260. Thereafter, the optical window is made to closely contact a predetermined position, that is, the circumference of the upper optical hole of the reaction chamber 210. When a process of forming a thin film on the substrate 270 with the photo-CVD apparatus is performed, a reaction gas is made to flow into the reaction chamber 210 through a reaction gas feed tube 216 and a nitrogen gas or an inert gas is made to flow into the fixing chamber 260 through an inlet 226, as much as a desired amount of flow. Then, light is irradiated from a light source 280 at the state where the two chambers 210 and 260 have no pressure difference. The gas in the two chambers 210 and 260 is discharged through outlets 218 and 228, respectively. By the above-described method, since the optical window is replaced at the state where the optical window fixing chamber 260 and the reaction chamber 210 are completely isolated from the optical window replacement chamber 220 by the gate valve 230, the reaction chamber 210 is not exposed to the atmosphere semi-permanently. Thus, since the inside of the reaction chamber 210 is not polluted by oxygen, nitrogen, dust or the like in the air, a high-quality thin film can be formed. Also, since there is no friction between the thin film attached optical window surface and the other portions during detachment and movement of the optical window, dust may not be generated to thus maintain the reaction chamber to be in the clean state continuously. Also, since the light source can be inserted in a vacuum, and a pressure difference applied to both sides of the optical window is little during formation of the thin film, a thin optical window can be used to thus make a large-area thin film forming apparatus.
As described above, in the FIG. 1 apparatus, the flexible curtain closely contacts the uppermost edge of the vertical wall surface in the reaction chamber and thus a space where a window purge cleaning gas flows between the flexible curtain and the optical window is isolated from the reaction chamber. However, since the sealing is not perfect, a blur phenomenon of the optical window cannot be effectively removed during deposition of a thin film. Also, when the flexible curtain is wound up in order to replace it with a new one during performing a thin film deposition or after completion of the thin film deposition, dust may be generated due to a friction with the uppermost edge of the reaction chamber wall surface closely contacting the flexible curtain. Also, in this apparatus, the optical window should be thick so that it can resist against the atmosphere. In addition, since an optical window purge cleaning gas is made to flow between the optical window and the flexible curtain, light absorption losses in the optical window and the purge cleaning gas cannot be ignored. Since this problem becomes further serious as the apparatus becomes larger, it is not nearly possible to fabricate a large-area apparatus with the structure that a light source is placed in the air and light is irradiated into the reaction chamber through the optical window. Also, a light source for emitting a vacuum ultraviolet light ray cannot be used with the structure that the light source is placed in the air. In order to solve the above-described problem, a structure that a light source is put in a space where an optical window purge cleaning gas flows, is disclosed in U.S. Pat. No. 4,654,226. By doing so, the optical window need not be used and it is possible to fabricate the large-area apparatus and use the vacuum ultra-violet light source. However, even in the structure of the light source placed in the vacuum, the surface of the light source cannot be prevented from being blurred by the material produced by the photo-chemical reaction due to the imperfect sealing between the reaction chamber and the flexible curtain as described above.
Meanwhile, according to the FIG. 2 apparatus, a large-area thin film can be deposited. However, since a large-area optical window should be used as well in this case, the large-area thin optical window may be damaged during cleaning the large-area optical window physically, and it is also difficult to handle the large-area thin optical window. Thus, the optical window should be thick to a degree. Accordingly, the light absorption loss in the optical window cannot but increase. Also, a vacuum should be broken in an optical window replacement chamber every time when the optical window need to be replaced and the polluted optical window should be replaced with a cleaned optical window. Then, the optical window replacement chamber is discharged to be a high vacuum state. As a result, the working ratio of the apparatus becomes low.